This invention is directed, in part, to novel dispersed hydrated sodium borate compositions, as well as additive packages and finished oil compositions comprising the same. The dispersed hydrated sodium borate compositions of this invention exhibit decreased turbidity over conventional dispersed hydrated sodium borate compositions and show good compatibility with additives typically used in fully formulated gear oil compositions. The finished oil compositions comprising such dispersed hydrated sodium borate compositions exhibit improved water tolerance with good storage stability.
This invention is also directed, in part, to methods for decreasing the turbidity of dispersed hydrated sodium borate compositions, and for improving the water tolerance of finished oil compositions comprising such dispersed hydrated sodium borate compositions.
The following references are cited in this application as superscript numbers:
1 Peeler, U.S. Pat. No. 3,313,727, Alkali Metal Borate E.P. Lubricants, issued Apr. 11, 1967
2 Adams, U.S. Pat. No. 3,912,643, Lubricant Containing Neutralized Alkali Metal Borates, issued Oct. 14, 1975
3 Sims, U.S. Pat. No. 3,819,521, Lubricant Containing Dispersed Borate and a Polyol, issued Jun. 25, 1974
4 Adams, U.S. Pat. No. 3,853,772, Lubricant Containing Alkali Metal Borate Dispersed with a Mixture of Dispersants, issued Dec. 10, 1974
5 Adams, U.S. Pat. No. 3,997,454, Lubricant Containing Potassium Borate, issued Dec. 14, 1976
6 Adams, U.S. Pat. No. 4,089,790, Synergistic Combinations of Hydrated Potassium Borate, Antiwear Agents, and Organic Sulfide Antioxidants, issued May 16, 1978
7 Adams, U.S. Pat. No. 4,163,729, Synergistic Combinations of Hydrated Potassium Borate, Antiwear Agents, and Organic Sulfide Antioxidants, issued Aug. 7, 1979
8 Frost, U.S. Pat. No. 4,263,155, Lubricant Composition Containing an Alkali Metal Borate and a Sulfur-Containing Polyhydroxy Compound, U.S. Pat. No. 5,461,184, issued Oct. 24, 1995
9 Frost, U.S. Pat. No. 4,401,580, Lubricant Composition Containing an Alkali Metal Borate and an Ester-Polyol Compound, issued Aug. 30, 1983
10 Frost, U.S. Pat. No. 4,472,288, Lubricant Composition Containing an Alkali Metal Borate and an Oil-Soluble Amine Salt of a Phosphorus Compound, issued Sep. 18, 1984
11 Clark, U.S. Pat. No. 4,584,873, Automotive Friction Reducing Composition, issued Aug. 13, 1985
12 Brewster, U.S. Pat. No. 3,489,619, Heat Transfer and Quench Oil, issued Jan. 13, 1970.
All of the above references are herein incorporated by reference in their entirety to the same extent as if each individual publication or patent was specifically and individually indicated to be incorporated by reference in its entirety.
High load conditions often occur in gear sets such as those used in automobile transmissions and differentials, pneumatic tools, gas compressors, centrifuges, high-pressure hydraulic systems, metal working and similar devices, as well as in many types of bearings. When employed in such environments, it is conventional to add an extreme-pressure (E.P.) agent to the lubricant composition and, in this regard, alkali metal borates are well known extreme-pressure agents for such compositions.1-11 E.P. agents are added to lubricants to prevent destructive metal-to-metal contact in the lubrication of moving surfaces. While under normal conditions termed xe2x80x9chydrodynamicxe2x80x9d, a film of lubricant is maintained between the relatively moving surfaces governed by lubricant parameters, and principally viscosity. However, when load is increased, clearance between the surfaces are reduced, or when speeds of moving surfaces are such that the film of oil cannot be maintained, the condition of xe2x80x9cboundary lubricationxe2x80x9d is reached; governed largely by the parameters of the contacting surfaces. At still more severe conditions significant destructive contact manifests itself in various forms such as welding, scoring, scuffing, ridging, rippling or cleavage. It is the role of E.P. additives to prevent this from happening. For the most part, E.P. agents have been oil soluble or easily dispersed as a stable dispersion in the oil, and largely have been organic compounds chemically reacted to contain sulfur, halogen (principally chlorine), phosphorous, carboxyl, or carboxylate salt groups which react with the metal surface under boundary lubrication conditions. Stable dispersions of hydrated metal borates have also been found to be effective as E.P. agents.
Because hydrated alkali metal borates are insoluble in lubricant oil media, it is necessary to incorporate the borate as a dispersion in the oil and homogenous dispersions are particularly desirable. The degree of formation of a homogenous dispersion can be correlated to the turbidity of the oil after addition of the hydrated alkali metal borate with higher turbidity correlating to less homogenous dispersions. In order to facilitate formation of such a homogenous dispersion, it is conventional to include a dispersant in such compositions. Examples of dispersants include lipophilic surface-active agents such as alkenyl succinimides or other nitrogen containing dispersants as well as alkenyl succinates.1-4, 12 It is also conventional to employ the alkali metal borate at particle sizes of less than 1 micron in order to facilitate the formation of the homogenous dispersion.11 
Of the hydrated alkali metal borates heretofore used, hydrated potassium borates were conventionally employed. The hydrated potassium borate compositions, additive packages, and lubricant compositions comprising such borates often had unacceptably high turbidity when added to lubricant compositions.
In addition, the hydrated potassium borate compositions, additive packages and lubricant compositions comprising hydrated potassium borates often had poor water tolerance. Such intolerance was reflected by the formation of borate crystals that generally separate from the oil phase to form deposits that can damage the elastomer seals in various engine parts and cause leakage.
In view of the above, further reductions in turbidity and further improvements in water tolerance for oil compositions comprising a sodium borate would be particularly beneficial.
This invention is directed to the novel and unexpected discovery that the turbidity arising from the preparation of a dispersed hydrated sodium borate composition can be reduced by specifically controlling the degree of dehydration of the boron in the dispersion.
In addition, this invention is directed to the novel and unexpected discovery that the water tolerance of dispersed hydrated sodium borates is improved by carefully controlling the ratio of sodium to boron and the degree of dehydration in the composition.
Accordingly, in one of its composition aspects, this invention is directed to a dispersed hydrated sodium borate composition comprising a hydrated sodium borate, a dispersant, optionally a detergent, and an oil of lubricating viscosity wherein said hydrated sodium borate is characterized by a hydroxyl:boron ratio (OH:B) of from about 0.80:1 to 1.60:1 and by a sodium to boron ratio of from about 1:2.75 to 1:3.25.
In one preferred embodiment, the dispersed sodium borate compositions described herein have a turbidity of less than about 75 ntu, more preferably, less than about 60 ntu, and still more preferably, less than about 40 ntu.
In another preferred embodiment, the dispersed hydrated sodium borate composition has a sodium to boron metal ratio of from about 1:2.9 to about 1:3.1 and more preferably about 1:3.
In still another preferred embodiment, the hydroxyl:boron ratio is from about 0.90:1 to 1.50:1, more preferably 1.00:1 to 1.40:1.
In yet another preferred embodiment, the hydrated sodium borate has an average particle size of less than about 0.3 microns and more preferably from about 0.10 to about 0.20 microns.
Preferably, the dispersed sodium borate compositions contain small amounts of a water-soluble oxo anion. Only from 0.001 moles to 0.11 moles of water soluble oxo anion should be present per mole of boron. This water-soluble oxo anion can include nitrate, sulfate, carbonate, phosphate, pyrophosphate, silicate, aluminate, germanate, stannate, zincate, plumbate, titanate, molybdate, tungstate, vanadate, niobate, tantalate, uranates, or can include the isopolymolybdates and isopolytungstates, or the hetcropolymolybdates and heteropolytungstates, or mixtures thereof.
Preferably the dispersant in said sodium borate compositions is selected from the group consisting of a polyalkylene succinimide, a polyalkylene succinic anhydride, a polyalkylene succinic acid, a mono- or di-salt of a polyalkylene succinic acid and mixtures thereof. Preferably, the dispersed sodium borate composition contains a detergent such as a metal sulfonate, preferably an alkylaromatic or polyisobutenyl calcium sulfonate which acts in these compositions to help provide for a homogeneous dispersion.
Another aspect of this invention is directed to additive packages comprising from about 10 to 75 weight percent of the dispersed hydrated sodium borate composition described above and from about 90 to 15 weight percent of one or more of conventional additives selected from the group consisting of ashless dispersants (0-5%), detergents (0-2%), sulfurized hydrocarbons (0-30%), dialkyl hydrogen phosphates (0-10%), zinc dithiophosphates (0-20%), pentaerythritol monooleate (0-10%), 2,5-dimercaptothiadiazole (0-5%), benzotriazole (0-5%), dispersed molybdenum disulfide (0-5%), foam inhibitors (0-2%), and imidazolines (0-10%) and the like wherein each weight percent is based on the total weight of the composition. It is understood of course, that the addition of such conventional additives will dilute the concentration of the hydrated sodium borate, dispersant and oil of lubricating viscosity in the dispersed hydrated sodium borate composition.
Such additive packages can be added in effective amounts to an oil of lubricating viscosity to form a finished oil composition. Accordingly, the finished oil compositions of this invention contain the additive packages as described above upon further blending with an oil of lubricating viscosity. Preferably, the additive package described above, in an amount of from about 5 to 15 weight percent, is added to an oil of lubricating viscosity, in the amount of from about 85 to 95 weight percent, to provide for the finished gear oil composition wherein the weight percent of each component is based on the total weight of the composition. More preferably, added along with the oil of lubricating viscosity is a polymethacrylate viscosity index improver which is included at a level of 0-12% and/or a pour point depressant at a level of 0-1%, to form a finished oil wherein the weight percent of each of the viscosity index improver and pour point depressant is based on the total weight of the composition.
This invention is also directed to a method for providing lower turbidity for dispersed hydrated sodium borate compositions which method comprises carefully controlling the hydroxyl:boron ratio (OH:B) of the dispersed hydrated sodium borate in the range of from about 0.80:1 to 1.60:1 and a sodium to boron ratio of from about 1:2.75 to 1:3.25.
This invention is still further directed to a method for preparation of such dispersed sodium borate compositions which comprises:
mixing, under agitation, a mixture of an aqueous solution of boric acid and sodium hydroxide, where the stoichiometric ratio of the boric acid and the sodium hydroxide are selected to provide for a sodium to boron ratio in the product of from about 1:2.75 to 1:3.25, with an oil of lubricating viscosity and a dispersant, and then heating the mixture to remove sufficient water so as to produce a dispersed hydrated sodium borate having a OH:B ratio of from about 0.80:1 to about 1.60:1.